Communications traffic at network edges is increasing over time due to the rising demand for a range of high-bandwidth services by business and residential customers. This rising demand places an increasing requirement on access networks to deliver those services.
One type of network suitable for high-bandwidth services is a Passive Optical Network (PON). It is desirable that apparatus deployed at remote terminals of the network is “colourless”. This means that the apparatus deployed at remote terminals is not configured to operate at a particular wavelength but, instead, is capable of operating across a range of wavelengths. This allows an economy of scale in manufacturing the terminal apparatus. The configuration of the operating wavelength of a terminal is made by other apparatus in the network, external to the terminal
There are several different approaches to WDM-PONs with colourless transceivers. One approach is called self-seeding and is described in the paper “Directly Modulated Self-Seeding Reflective Semiconductor Optical Amplifiers as Colourless Transmitters in Wavelength Division Multiplexed Passive Optical Networks”, Wong et al, Journal of Lightwave Technology, Vol. 25, No. 1, January 2007. A Reflective Semiconductor Optical Amplifier (R-SOA) at a terminal generates broadband amplified spontaneous emission (ASE) light. The light is transmitted upstream. A wavelength division multiplexer (WDM) such as an Arrayed Waveguide Grating (AWG) at a remote node reflects a spectral slice of the broadband light back to the terminal for use as a seeding light. This locks the transmitted wavelength of the R-SOA. The R-SOA is directly modulated with upstream data. The operating wavelength of a remote terminal is determined by the WDM port that the terminal is connected to.
An improvement of the self seeded system uses a polarisation insensitive reflective device, such as a Faraday mirror, to reflect back to the transmitter a given portion of the emitted light, in order to create a sort of distributed cavity laser. Polarisation insensitivity helps to to ensure a stable performance. This improvement is described in WO 2012/034604 A1.
The use of self-seeding has so far been limited to networks with a tree-and-branch topology.